Chapter 5: Gases Flashcards
Barometer
A device for measuring atmospheric pressure
Manometer
A device for measuring the pressure of a gas in a container
BIG WHOPPER
1 atm = 760 mmHg = 29.92 inHg = 760 torr = 101325 Pa = 101.325 kPa = 14.69 psi
Boyle’s Law
PV = k
P1V1 = P2V2
Inverse relationship between pressure and volume
Charles’s Law
V = bT
V1/T1 = V2/T2
Direct relationship between temperature and volume
Avogadro’s Law
V = an
V1/n1 = V2/n2
Direct relationship between number of moles and volume
Universal gas constant
0.08206 L atm / K mol
Ideal gas law
PV = nRT
Molar volume of an ideal gas at 273 K and 1 atm
22.4 L
Standard temperature and pressure (STP)
0 degrees Celsius & 1 atm
Molar mass of a gas
dRT/P
Gas density unit
Grams per liter
Dalton’s Law of Partial Pressures
For a mixture of gases in a container, the total pressure exerted is the sum of the pressures that each gas would exert if it were alone.
Partial pressure
The pressure that a particular gas would exert if it were alone in the container
Mole fraction
The ratio of the number of moles of a given component in a mixture to the total number of moles in the mixture
x1 = n1/nTOTAL = P1/PTOTAL
Postulates of the Kinetic Molecular Theory
- The particles are so small compared with the distances between them that the volume of the individual particles can be assumed to be negligible (zero).
- The particles are in constant motion. The collisions of the particles with the walls of the container are the cause of the pressure exerted by the gas.
- The particles are assumed to exert no forces on each other; they are assumed neither to attract nor to repel each other.
- The average kinetic energy of a collection of gas particles is assumed to be directly proportional to the Kelvin temperature of the gas.
Root Mean Square Velocity
√3RT/M R = 8.3145 J/K mol (J = joule = kg m^2/s^2) T = temperature of gas (in K) M = mass of a mole of gas in kg Final units are in m/s.
Diffusion
Mixing of gases
Effusion
The passage of a gas through a tiny orifice into an evacuated chamber
Graham’s Law of Effusion
Rate of effusion for gas 1/Rate of effusion for gas 2 =
√M2/√M1
We must correct for non-ideal gas behavior when:
- The pressure of the gas is high.
2. The temperature is low.
Under the conditions of real gases:
- Concentration of gas particles is high.
2. Attractive forces become important.
Van der Waals Equation
[Pobs + a(n/V)^2] x (V-nb) = nRT
For a real gas the _________ is lower than __________.
Actual observed pressure; the ideal pressure
